The present invention relates to a nickel plated steel sheet and the manufacturing method thereof wherein it is planned to prevent adhesion of steel sheet with each other, which is apt to occur during producing a steel sheet (shown as diffused nickel diffused plated steel sheet, herein after) in which nickel is diffused by heat treatment of a nickel plated steel sheet in an annealing furnace.
Generally, a nickel diffused plated steel sheet is rewound as a tight coil after plating, and then is heat treated in a box-annealing furnace around 500-700.degree. C. in order to give workability. However, this heat treatment causes a problem that since diffusion of nickel on the steel sheet surface proceeds, rewound and stacked steel sheets adhere with each other. Therefore, conventionally, heat treatment preventing direct contact of steel sheets with each other has been carried out in such a way that steel sheet is annealed in the openly coiled state where steel sheet is coiled with a wire or the like as a spacer which makes gap between rewound steel sheets, or it is annealed in the state where it is previously coated with a releasing agent such as an oxide, a carbide, or a nitride which are stable in high temperature.
However, the method of annealing in the state that steel sheet is rewound with a wire stacking to it is not efficient since it is apt to be scratched and requires extra work for rewinding and removing of the wire. Moreover, the annealing method with coating of releasing agent on a steel sheet surface has some problems such as the increment of cost by using a releasing agent, difficulty of removing of the releasing agent, and visual affection of the steel sheet surface, and therefore either method lacks industrial practicability.
The prevention of adhesion of a cold rolled steel plate during annealing, that is not for nickel plated steel sheet, is practiced by coating a releasing agent such as oxide of titanium or aluminum on the steel sheet surface (laid-open Japanese patent Sho 63-235427 and so on).
However, since these oxides are remained on the steel sheet surface after annealing, it has a disadvantage of deteriorated appearance of steel surface caused by affected color tone. For these reasons, the above-mentioned wire has been used in the heat treatment of a nickel plated steel sheet but oxide has not been used.
It is a technical objective of the present invention to provide a nickel plated steel sheet treated for the prevention of adhesion in order to suppress adhesion of the plated steel sheets with each other during the heat treatment of the steel sheet plated with nickel.
The nickel plated steel sheet of the present invention does not need rewinding of a wire or coating of a releasing agent for the prevention of adhesion and can have superior appearance after the heat treatment.